The stability of Shadowplay has always been hit and miss... and then crash. It's a hell of a lot more stable than it used to be and when it worked it was pretty nice for the small performance hit. But I haven't used it in a long time. I tried out Nvidia's broadcasting to Youtube, which is pretty new, but it was hugely crashy. They might have improved it in the last Experience update, but I'm pretty much good with with OBS right now for the most part. Even if streaming and being lazy about it is lower quality than recording since it's restricted to much lower bandwidth.
But again, when Shadowplay is stable, it is pretty nice, if you don't REALLY want the losslessness of FRAPS (or maybe even OBS recording set up properly).